Electro-chemical sensor

Abstract

The present invention provides an electrochemical sensor having a solid electrically conductive substrate and a compound immobilized thereon which has binding affinity for an analyte species to be detected and also displays electrochemical behavior which is modified upon binding of that analyte species, so that binding of an analyte species can be detected by measuring electrochemical properties, such as by voltammetry. Desirably the immobilized compound contains both a first moiety with binding affinity for the analyte and a separate second moiety which is a redox system whose electrochemical oxidation/reduction properties become modified when the first moiety binds the analyte. The analyte binding moiety may be a diol or polyol and preferably is a sugar. The electrochemical sensor finds use in methods of analyzing reservoir and process fluids, particularly at a subterranean location. The electrochemical sensor may be a component of a downhole tool, adapted for deployment downhole.

The invention claimed is: 
     
       1. A method of detecting an analyte species in a liquid, the analyte species being selected from ions of the non-metal B and ions of the metals Cu, Fe, Co, Ni, Ba, Ca, Sr, Mo, W, Zn, Cd, Hg, Mg, Ra, Pb, Pd, Pt, and V, the method comprising: 
       providing an electrochemical sensor comprising:
 a solid electrically conductive substrate and 
 at least one compound immobilized thereon which contains both a sugar which is a di- or poly-hydroxy compound with binding affinity for the analyte species to be detected and a non-sugar redox system which displays electrochemical oxidation/reduction behaviour which is modified when the sugar binds the analyte species to be detected,
 wherein the sugar and the non-sugar redox system are connected directly or indirectly through one or more covalent bonds 
 
 
       contacting the liquid with the sensor, for binding of the analyte to the said compound immobilized on the substrate, and 
       measuring the electrochemical oxidation/reduction behaviour of the redox system of said compound immobilized on the substrate. 
     
     
       2. A method according to  claim 1  wherein measurement of the electrochemical oxidation/reduction behaviour of the redox system of the said immobilised compound is carried out by voltammetry. 
     
     
       3. A method according to  claim 1  wherein the ionic analyte species is selected from ions of the metals Ca, Mg, Ba, Sr, Ra and Fe. 
     
     
       4. A method according to  claim 1  wherein the sugar has a five or six membered carbohydrate ring. 
     
     
       5. A method according to  claim 1  wherein the sugar has a five or six membered carbohydrate ring with modifications to one, two or three of the hydroxyl groups of the carbohydrate ring. 
     
     
       6. A method according to  claim 1  wherein the liquid is a subterranean water body and the sensor is incorporated in a tool suspended in a well communicating with the subterranean water body. 
     
     
       7. A method according to  claim 1  wherein the liquid is in a wellbore and the sensor is in a tool suspended in the wellbore. 
     
     
       8. A method according to  claim 1  wherein the tool is a wireline tool or a slickline tool. 
     
     
       9. A method according to  claim 1  wherein the redox system undergoes electrochemical oxidation and reduction reactions in aqueous solution, and properties of the reactions are altered when the sugar binds the analyte. 
     
     
       10. A method according to  claim 9  wherein voltages at which maximum redox reaction occurs are altered when the first moiety binds the analyte and measurement of the electrochemical oxidation/reduction behaviour of the redox system of the said immobilised compound is carried out by voltammetry. 
     
     
       11. A method of detecting an ionic analyte species in a liquid, the analyte species being selected from ions of the non-metal B and ions of the metals Ca, Cu, Fe, Co, Ni, Ba, Ca, Sr, Mo, W, Zn, Cd, Hg, Mg, Ra, Pb, Pd, Pt, and V, the method comprising: 
       providing an electrochemical sensor comprising:
 a solid electrically conductive substrate and 
 at least one compound immobilized thereon which has binding affinity for an ionic analyte species to be detected and displays electrochemical oxidation/reduction behaviour which is modified upon binding of the analyte,
 wherein the compound contains both a first moiety with binding affinity for the analyte and a second moiety which is a redox system connected to the first moiety through one or more covalent bonds and whose electrochemical oxidation/reduction properties become modified when the first moiety binds the analyte, 
 
 
       contacting the liquid with the sensor, for binding of the analyte to the said compound immobilized on the substrate, and 
       measuring the electrochemical oxidation/reduction behaviour of the redox system of the said compound immobilized on the substrate. 
     
     
       12. A method according to  claim 11  wherein measurement of the electrochemical oxidation/reduction behaviour of the redox system of the said immobilised compound is carried out by voltammetry. 
     
     
       13. A method according to  claim 11  wherein the ionic analyte species is selected from ions of the metals Ca, Mg, Ba, Sr, Ra and Fe. 
     
     
       14. A method according to  claim 11  wherein the conductive substrate is carbon-based. 
     
     
       15. A method according to  claim 11  wherein the redox system displays electrochemical oxidation and reduction when in contact with aqueous solution having pH in the range from pH 4 to pH 10. 
     
     
       16. A method according to  claim 11  wherein the redox system is a metallocene. 
     
     
       17. A method according to  claim 11  wherein the liquid is a subterranean water body and the sensor is incorporated in a tool suspended in a well communicating with the subterranean water body. 
     
     
       18. A method according to  claim 11  wherein the redox system undergoes electrochemical oxidation and reduction reactions in aqueous solution, and properties of the reactions are altered when the first moiety binds the analyte. 
     
     
       19. A method according to  claim 18  wherein voltages at which maximum redox reaction occurs are altered when the first moiety binds the analyte and measurement of the electrochemical oxidation/reduction behaviour of the redox system of the said immobilised compound is carried out by voltammetry. 
     
     
       20. A method according to  claim 11  wherein the liquid is in a wellbore and the sensor is in a tool suspended in the wellbore. 
     
     
       21. A method according to  claim 20  wherein the tool is a wireline tool or a slickline tool.